Examples of a charged particle beam device include a scanning electron microscope (hereinafter referred to as SEM), an electron probe micro analyzer (EPMA), an electron beam welder, an electron beam writing device, and an ion beam microscope.
Conventional SEMs include lenses that are each configured to have a short focus for a higher resolution. Increasing resolution requires increasing the magnetic flux density for the magnetic flux density distribution B(z) of the lens along the optical axis. Increasing resolution also requires decreasing the thickness of the lens, that is, the z width for the magnetic flux density distribution.
Patent Literature 1 below discloses an SEM including two objective lenses (namely, a first objective lens and a second objective lens). Hereinafter, a lens on the electron gun side of a sample is referred to as first objective lens, whereas a lens on the side opposite to the electron gun side of a sample is referred to as second objective lens. The second objective lens is used particularly in a high-resolution observation mode in which the accelerating voltage Vacc is low, specifically, within a range of 0.5 kV to 5 kV. The first objective lens is used in a normal observation mode in which the accelerating voltage Vacc is within a range of 0.5 kV to 30 kV.
The technique disclosed in Patent Literature 1 below does not allow the first objective lens and the second objective lens to operate simultaneously. The first objective lens and the second objective lens are switched by a mode switching means in accordance with the mode. Patent Literature 1 below also discloses in the second embodiment (see paragraph [0017]) separating part of the magnetic poles of the second objective lens from the rest with use of an electric insulator in terms of electric current and electric potential. A voltage Vdecel is applied between the part of the magnetic poles and the sample.
Patent Literature 1 below discloses in the first embodiment (paragraphs [0010] to [0016]) disposing a secondary electron (or backscattered electron) detector at a position closer to the electron gun than the first objective lens is. Secondary electrons (or backscattered electrons) generated by the sample pass through the first objective lens and enter the detector.
Patent Literature 2 below also discloses an SEM configuration. The SEM of Patent Literature 2 is configured to include an objective lens disposed on the side of a sample which side is opposite to the electron gun side. Secondary electrons are deflected by an attracting electric field of a secondary electron detector and captured by the secondary electron detector.